The Beam Research Program at Lawrence Liver-more National Laboratory is continuing development of the dielectric wall accelerator (DWA), a type of accelerator which uses stacked pulse-forming lines (PFLs) to apply an accelerating field directly to the beam through a nonconducting vacuum boundary. Here, we report operation of a DWA as an electron diode using a surface flashover plasma cathode. Peak perveances in excess of 6 x 10(-6) A/V-3/2 were measured, with current extraction and pulse train format depending on flashover source timing and PFL switching speed.

Compact dielectric wall (DWA) accelerator technology is being developed at the Lawrence Livermore National Laboratory. The DWA accelerator uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube. Its high electric field gradients are achieved by the use of alternating insulators and conductors and short pulse times. The DWA concept can be applied to accelerate charge particle beams with any charge to mass ratio and energy. Based on the DWA system, a novel compact proton therapy accelerator is being developed. This proton therapy system will produce individual pulses that can be varied in intensity, energy and spot width. The system will be capable of being sited in a conventional linac vault and provide intensity modulated rotational therapy. The status of the developmental new technologies that make the compact system possible will be reviewed. These include, high gradient vacuum insulators, solid dielectric materials, SiC photoconductive switches and compact proton sources. Applications of the DWA accelerator to problems in homeland security will also be discussed.

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is being developed for a variety of applications. Research describing an extreme variant of this technology aimed at producing a compact, variable output linear accelerator for proton therapy for cancer will be described along with the technical challenges and issues. The goal of the development is to produce a proton accelerator that will fit in a standard linac vault and deliver intensity modulated proton therapy. Tomotherapy, Inc. has licensed the new accelerator technology from the Lawrence Livermore National Laboratory and the Compact Particle Acceleration Corporation (CPAC) is supporting development of the system. Research sponsored by Tomotherapy, Inc. and CPAC. Conflict of Interest: Some of the co‐authors have a financial interest in Tomotherapy, Inc. and/or CPAC.

Large aperture plasma electrode pockels cells (PEPC) are an enabling technology in the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory. The Pockels cell allows the NIF laser to take advantage of multi-pass amplifier architecture, thus reducing costs and physical size of the facility. Each Pockels cell comprises four 40-cm times 40-cm apertures arranged in a 4times1 array. The combination of the Pockels cell and a thin-film polarizer, configured in a 4times1 array, form an optical switch that is key to achieving multi-pass operation. Solid-state Plasma Pulse Generators (PPGs) and high current high voltage solid-state Switch Pulse Generators (SPGs) have been developed for use in the PEPC. The solid-state plasma pulse generators initiate and maintain plasma within the cells; each pulser is capable of delivering 60 J of energy to each plasma channel. Deployment of the solid-state PPGs has been completed in NIF. The MOSFET-switched SPG is capable of delivering a requisite fast rise time, 17 kV flattop pulse to the cells' nonlinear crystals. A complete software and hardware control system has been developed and is currently being tested for use on the solid-state SPGs. Also a transmission line modeling, development, and testing effort is in process, in support of NIFs' Advanced Radiographic Capabilities (ARC). Work is scheduled for completion by the end of the calendar year.

Summary form only given. A high current, high voltage, all solid-state pulse modulator has been developed for use in the Plasma Electrode Pockels Cell (PEPC) subsystem in the National Ignition Facility. The MOSFET-switched pulse generator, designed to be a more capable plug-in replacement for the thyratron-svvitched units currently deployed in NIF, offers unprecedented capabilities including burst-mode operation, pulse width agility and a steady-state pulse repetition frequency exceeding 1 Hz. Capable of delivering requisite fast risetime, 17-kV flattop pulses into a 6-Omega load, the pulser employs a modular architecture characteristic of the inductive adder technology, pioneered at LLNL for use in acceleration applications, which keeps primary voltages low (and well within the capabilities of existing FET technology), reduces fabrication costs and is amenable to rapid assembly and quick field repairs.

As the switching capabilities of solid-state devices increase, these devices are being incorporated into modulator designs for high voltage accelerator applications. Solid-state modulators based on inductive adder circuit topology have demonstrated great versatility with regard to pulse width and pulse repetition rate while maintaining fast pulse rise and fall times. Additionally, these modulators are capable of being scaled to higher output voltage and power levels. An explanation of the basic circuit operation will be presented as well as test data of several different hardware systems.

The ability to extract particle beam bunches from a ring accelerator in arbitrary order can greatly extend an accelerator's capabilities and applications. A prototype solid-state kicker pulser capable of generating asynchronous bursts of 50 kV pulses has been designed and tested into a 50 /spl Omega/ load. The pulser features fast rise and fall times and is capable of generating an arbitrary pattern of pulses with a maximum burst frequency exceeding 5 MHz. If required, the pulse-width of each pulse in the burst is independently adjustable. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. Test data, capabilities, and limitations of the prototype pulser are described.

Single solid-state devices or arrays of solid-state devices are being incorporated into many pulsed power applications as a means of generating fast, high-power, high repetition-rate pulses and ultimately replacing hard tubes and thyratrons. While vendors' data sheets provide a starting point for selecting solid-state devices, most data sheets do not have sufficient information to determine performance in a pulsed application. To obtain this relevant information, MOSFET's and IGBT's from a number of vendors have been tested to determine rise times, fall times and current handling capabilities. The emphasis is on the evaluation of devices that can perform in the range of 100 ns pulse widths and the test devices must be capable of switching 1000 volts or greater at a pulsed current of at least 25 amperes. Additionally, some devices were retested with a series magnetic switch to evaluate the effects on switching parameters and specifically rise times. All devices were evaluated under identical conditions and the complete test results are presented.

To replace a hard tube design, a solid-state kicker pulser for the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-2) has been designed and tested. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. The modulator features very fast rise and fall times, pulse width agility and a high pulse-repetition rate in burst mode. The modulator can drive a 50 /spl Omega/ load with voltages up to 20 kV and can be easily configured for either positive or negative polarity. The presentation includes test and operational data.

An all solid-state kicker modulator for the Dual-Axis Radiographic Hydrodynamic Test facility (DARHT-2) has been designed and tested. This kicker modulator uses multiple solid-state modules stacked in an inductive-adder configuration where the energy is switched into each section of the adder by a parallel array of MOSFETs. The modulator features very fast rise and fall times, pulse width agility and a high pulse-repetition rate in burst mode. The modulator can drive a 50* cable with voltages up to 20 kV and can be easily configured for either positive or negative polarity. The presentation will include test data collected from both the ETA II accelerator kicker and resistive dummy loads.

Researchers at the Lawrence Livermore National Laboratory (LLNL) are developing a flexible, all solid-state pulsed power source that will enable an induction accelerator to produce mulitkiloampere electron beams at a maximum pulse repetition frequency (prf) of 2 MHz. The prototype source consists of three, 15-kV, 4.8-kA solid-state modulators stacked in an induction adder configuration. Each modulator contains over 1300 field-effect transistors (FETs) that quickly connect and disconnect four banks of energy storage capacitors to a magnetic induction core. The FETs are commanded on and off by an optical signal that determines the duration of the accelerating pulse. Further electronic circuitry is provided that resets the magnetic cores in each modulator immediately after the accelerating pulse. The system produces bursts of five or more pulses with an adjustable pulse width that ranges from 200 ns to 2 mu s. The pulse duty factor within a burst can be as high as 25% while still allowing time for the induction core to reset. The solid-state modulator described above is called ARM-II and is named for the Advanced Radiographic Machine (ARM)-a powerful radiographic accelerator that will be the principal diagnostic device for the future Advanced Hydrotest Facility (AHF).

A new high speed optical control, diagnostic and power supply system has been developed for a solid state induction modulator. The modulator consists of a large array of field effect transistors (FETs) that switch a high-voltage pulse across a tape-wound magnetic core. The FETs within the modulator are mounted on numerous circuit boards that are stacked in series for high-voltage operation. The new optical system overcomes the issue of voltage isolation by supplying each circuit board with optically coupled control power and high bandwidth signal information. An optical fiber is used to transmit laser light to a custom photovoltaic cell that provides DC power to the on-board control circuits. Optical fiber technology is again used to convey a pulse that contains detailed analog features to the FET gate controls. Diagnostic data and status information are also obtained from each board by similar optical methods.

Lawrence Livermore National Laboratory (LLNL) and EG&G Energy Measurements are developing a new solid-state power system for two proposed accelerators. One of the accelerators is a circular arrangement of induction cells called a recirculator for accelerating heavy ions for inertial fusion, the other is a linear induction accelerator for electron beams called the Advanced Radiographic Machine (ARM). The need for complex pulse agility in these accelerators led us to examine solid-state switching components that have an on/off capability. The intrinsic speed of solid-state switching satisfies our high PRF requirements, while the on/off switching action of some semiconductor devices enables us to select an arbitrary pulse width. To accommodate these requirements, we selected field effect transistors (FETs) as the preferred switching elements. The same FET switching technology applies to both accelerators due to their similar pulse requirements. For our research, two full-scale prototypes were built-a 5 kV induction recirculator cell and a single 15 kV induction modulator for the ARM accelerator. We discuss the general network features that are common to both machines, followed by performance and modeling data.